E arlier this year, Mercury HiPerformance made

dreams come true when it officially introduced the EFI version of the hugely successful HP500 engine package. in addition to the super-trick, multiport electronic fuel-injection system that replaced the old 850 cfm Holiey four-barreled carb, the new HP500 EFI also got a slight cam change, a few upgraded internal parts and some really sexy-looking blue-anodized hardware pieces. Although pricey, how can you resist? It’s 470 propshaft horsepower and

502 cubic inches with all the reliability and driver-friendly characteristics that MerCruisers production-line MPI engines have become known for.

But some hot-boaters just can’t leave well enough alone, and that’s where innovative companies like Whipple Industries come into play. Just when you think you’ve got the absolute very best, newest, most trick engine combination possible, they develop, manufacture and market something even better.

So let’s put it to the test. Whipple has a brand-new supercharging kit for MerCruiser’s HP500 EEl package, which is quite a feat in itself, since adding a blower to an EFI motor is a lot more corn-

sleek Eliminator Daytona turned a very impressive radar 91 mph at 5,200 rpm. We didn’t do any out-of-the-hole acceleration numbers, since drag racing is not what Bravo One drives were designed for. Still, the pushed-back-in-your-seat feel from 35 to 80 mph was invigorating, to say the least. Even in stock configuration, this has to be one of the hottest-run - fling hull/engine combinations around.

With the baseline numbers now complete, it was off to GT Performance Products for some dyno numbers. Remember, the new stock HP500 EFI is still rated at 470 pshp. As the installation of the Whipple HP500 kit is being done, here’s a rundown of the package. To start with, Whipple gives you a new 2,100 cfm throttle body with a Coast Guard-approved flame arrester. The progressive throttle-linkage setup has all the features of the stock MerCruiser. You also get a special intercooler made by Whip- pie. This one is really effective and very corrosion-resistant, since it’s made from cupronickel instead of aluminum and the internal cooling fins are copper. This intercooler is definitely

however, is Whipple’s custom interface computer system, which has its own built-in barometer and thermometer and measures the air by weight. This allows you to run a variety of boost pressures (from one to ten pounds), as the

of “fail-safe” sensors/monitors Dfl line to guard against detoiation, overheating, low oil Dressure, etc. And, of course, the kit also provides a Whipplecharger screw-type cornpressor (supercharger) with belts, pulleys and adapters. It is,

NEVER ENOUGH

plicated than making one work with a conventional carburetor. Although we did dyno comparison tests of the HP500 EFI before and after, thanks to GT Performance Products (Gary Teague) of Montclair, California, we also needed to “before and after” the project on the water in a real boat. Thanks again go to Bob Leach at Eliminator Boats, who jumped at the chance to supply us with a new 22 Daytona air-entrapment tunnel for the comparison.

In box-stock condition with a Bravo One drive, 1.5:1 gear ratio and a 30-pitch prop, the

What would it be like to Whipplecharge MerCruiser’s HP500 EFI? The answer:

awesome!

STORY AND PHOTOGRAPHY

BY BOB BROWN

designed to do some heavy- duty air-temperature reduction, which does nothing but help increase horsepower and minimize the chance of detonation. The real key to this kit,

its own right, a highly efficient, very positive system (at full boost before 2,000 rpm). Okay, hold your breath! The whole package only runs approximately $6,495, suggested retail. Now comes the good part.

On the dyno, the stock HP500 EFI puts out close to 500 horsepower in the 5,000- to 5,200-rpm range. Remember, MerCruiser rates it at only 470 measured at the propshaft, not the crankshaft. Our dyno tests were done at six pounds maximum boost, which Whip- pie feels is a good level, especially it you still want to run

computer automatically compensates and recalibrates the critical air/fuel mixture to just the right ratio, even it you go boating at different elevations. You also still have a number